Automated mailpiece fabrication employs a variety of systems, devices and processes dedicated to perform specific sheet/media handling operations. These may include, inter alia, (i) mailpiece inserters dedicated to insert/fill envelopes with mailpiece content material, (ii) mailing machines/meters adapted to perform additional processing tasks such as moistening/sealing the envelope flap, weighing the completed/finished mailpiece, and applying/printing postage indicia for mailpiece delivery and (iii) envelope printing apparatus (both in-line and shuttle type) adapted to rapidly print mailpiece information (e.g., destination and return addresses) on a face of the envelope. When processing a small number of mailpieces or insufficient number to obtain “sorted mail” discounts (i.e., available through the Manifest Mailing System (MMS)), printed mailpieces are typically allowed to randomly fall into an open container. Alternatively, when printing a large number of conventional-size mailpieces (i.e., type ten envelopes) eligible for USPS sorted mail discounts, the printed mailpieces may be neatly shingled and stacked for subsequent containment within a tray container.
The process of stacking/arranging mailpieces suitable for sorted mail discounts may be performed by a conveyor stacker, such as the type described in Sloan Jr. et al. U.S. Pat. No. 6,817,608. The stacker is an upright module having a conveyor system (i.e., a deck defined by one or more conveyor belts) which is disposed adjacent to, and essentially co-planar with, the output of the mailpiece printer. The conveyor system defines a feed path which is at right angles to, or essentially orthogonal with, the output path of the printer and includes stepped upstream and downstream segments. The upstream segment is vertically raised and operates at an increased speed relative to the downstream segment. As mailpieces exit the printer, the conveyor deck of the upstream segment receives mailpieces such that a space or gap is created between adjacent mailpieces. As the mailpieces move from the upstream to downstream segments, the mailpieces traverse a vertical step produced by the height differential between the segments. Inasmuch as the conveyor speed of the downstream segment is reduced relative to the upstream segment, mailpieces fall one atop another and shingle as the downstream segment slowly moves the mailpieces away from the vertical step. As the mailpieces continue downstream, a wedge or stacking ramp causes the mailpieces to assume an on-edge orientation to augment the removal and stacking of mailpieces within a tray container.
In addition to effecting the desired mailpiece arrangement and orientation, the conveyor stacker may include a high-output dryer for the purpose of drying the ink printed on the face of each mailpiece. The dryer is disposed over the conveyor deck of the upstream conveyor segment and produces a high-temperature flow of air over the face of each mailpiece. More specifically, the dryer includes a resistive heating element, one or more propulsive fans for directing ambient air over and around the heating element, and a louvered register for ducting the heated air over the mailpieces at a desired angle. With respect to the latter, the louvers of the register are disposed at an acute angle relative to the plane (i.e., substantially horizontal plane) defined by the underlying mailpieces. Specifically, the louvers are disposed at an angle of about thirty-five (35) degrees relative to the horizontal. As such, a horizontal component of the resultant airflow vector is produced which lies parallel to, and in the same direction as, the conveyor deck (i.e., movement of the mailpieces). A conveyor stacker, such as the type described above, is produced by Pitney Bowes Inc. of Stamford, Conn. under the tradename “DA400 Dryer/Stacker”.
The dryer functions to rapidly evaporate the ink solvent, thereby preventing the opportunity for the printed ink to smear or smudge when the face surfaces of the mailpieces are juxtaposed and/or contiguous, i.e., upon being shingled, raised on-edge and stacked. It will, therefore, be appreciated that the rate of mailpiece stacking is not solely a function of the conveyor deck speed, i.e., the speed of the upstream and downstream segments, but also a function of the rate of ink drying.
The rate of ink drying and associated print quality (e.g., the sharpness of the images edges) on the face of an envelope is a function of variety of factors including the efficacy of the drying apparatus, the characteristics of the ambient environment, and the properties of both the envelope and the ink. With respect to the dryer, factors include (i) the radiant heat energy produced by the heating element, (ii) the convective heat transfer between the heating element and the airflow produced by the propulsive fan(s), (iii) the convective heat transfer between the ink and the heated airflow due to the rate of air flowing over the envelope, i.e., the quantity of air moved by the propulsive fan(s), (iv) the convective heat transfer between the ink and the heated airflow due to the direction of air flowing over the envelope, i.e., through the louvers of the register, and (v) the proximity of the heating element to the envelope, i.e., the separation distance therebetween.
With respect to the characteristics of the ambient environment, factors include the ambient air conditions surrounding the dryer. For example, should humid conditions exist, e.g., 70% latent heat, evaporation will occur slowly and, so too, will the rate of ink drying. Concerning the properties of the paper and/or ink, factors affecting the drying time include, inter alia, (i) the type of paper used in the fabrication of the envelope, e.g., flat, satin, or glossy finish, etc., (ii) the evaporative properties of the ink solvent, and (iii) the viscous/molecular properties of the ink e.g., properties of the ink to flow, surface tension, etc. With respect to the viscous/molecular properties, a low viscosity, low surface tension ink will flow, spread or flatten when a bead or drop is applied to a surface. That is, the diameter and/or area of a circular drop will enlarge under the forces of gravity and/or due to the lack of strong molecular bonds. This increased area has the effect of increasing the surface area available for heat transfer, wicking action (into the underlying substrate material), and evaporation. Hence, an advantage of low viscosity/surface tension inks is their ability to dry rapidly. A disadvantage, however, relates to a decrease in edge sharpness, and commensurate reduction in print quality.
Dryers of the prior art offer a single solution to drying ink, i.e., a fixed geometric configuration for a variable set of conditions. Such prior art dryers are, therefore, non-optimum whenever unique conditions exist, or, alternatively, wherever conditions differ from those originally addressed by the dryer. For example, should a high viscosity, slow drying ink be employed to print envelopes, prior art dryers may be unable to provide the necessary heat transfer necessary to dry the ink, i.e., before contact between mailpieces causes smearing or smudging. Alternatively, prior art dryers may produce more than sufficient heat output to dry a low viscosity, fast drying ink. Consequently, an opportunity to reduce the power consumed by the dryer may be lost.
A need therefore exists, to provide a method and system for drying ink on a substrate material which produces an optimum heat output based upon a variety of sensed parameters.